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Nepal's Air Quality Crisis

From valley smog to hill fires — mapping the geography and causes of air pollution

Grades 8–10 45 min analysis live IESH data

Students analyse air quality patterns, investigate the specific causes of Nepal's urban and rural air pollution, and assess its health and economic burden using real data alongside sensor readings.

Learning objectives

  • Explain why Kathmandu Valley is particularly vulnerable to air pollution concentration.
  • Identify and categorise the main sources of air pollution in Nepal by sector.
  • Interpret the air quality index (AQI) scale and relate it to health effects.
  • Analyse the disproportionate health burden of air pollution across socioeconomic groups.

Background

Air pollution consists of gases (CO, NO₂, SO₂, ozone) and particles (PM10 and PM2.5, where the number refers to diameter in micrometres). PM2.5 — particles smaller than 2.5 µm — is considered the most dangerous because its tiny size allows it to penetrate deep into the lungs and enter the bloodstream. Sources in Nepal include vehicle exhaust (mostly old, poorly maintained diesel vehicles), brick kilns (operating a traditional Bull's Trench design rather than cleaner zigzag kilns), biomass burning, road dust and industrial activity.

Kathmandu's geography makes it especially prone to pollution accumulation. The valley sits at 1,400 m, surrounded by hills rising to 2,700 m on three sides. In winter, a temperature inversion forms — warm air sits above cold trapped air in the valley, acting like a lid that prevents vertical mixing. Pollutants accumulate in the trapped cold layer. This is the same meteorological mechanism responsible for the 1952 Great London Smog, which killed 4,000 people in four days.

Nepal's Department of Environment conducts air quality monitoring at a small number of stations. IQ Air's global ranking has placed Kathmandu among the world's 20 most polluted capitals in multiple recent years. The health cost is real: respiratory diseases, cardiovascular disease, low birth weight and reduced cognitive development in children are all linked to chronic PM2.5 exposure.

Procedure

  1. Record today's MQ-7 and MQ-135 readings and note the time of day and current weather conditions.
  2. Study the AQI reference table: Good (0–50), Moderate (51–100), Unhealthy for Sensitive Groups (101–150), Unhealthy (151–200), Very Unhealthy (201–300), Hazardous (301+).
  3. Research: what was Kathmandu's PM2.5 AQI on the worst day recorded in the last 5 years? What were people advised to do?
  4. List the FIVE main sources of air pollution in Nepal. For each, categorise it as: (a) indoor or outdoor, (b) urban or rural, (c) seasonal or year-round.
  5. Draw a simple diagram showing why cold air is trapped in Kathmandu Valley in winter (temperature inversion). Label: warm air layer, cold air layer, pollution trapped, valley walls.
  6. Calculate: if average Kathmandu PM2.5 is 50 µg/m³ and the WHO guideline is 15 µg/m³, by what percentage does Kathmandu exceed the guideline?

Discussion

  1. Poor families in Nepal are more likely to use biomass fuels, live near roads or brick kilns, and have less access to healthcare. How does air pollution become a poverty issue?
  2. Should the Nepali government prioritise reducing Kathmandu's outdoor pollution or Nepal's rural indoor pollution? What criteria would guide this decision?
  3. A school in Kathmandu is considering installing an air quality sensor in each classroom. What would the data be used for? What decisions could it inform?

Worksheet

1. Explain in your own words what a "temperature inversion" is and why it causes pollution to concentrate in Kathmandu Valley. [5 marks]

Answer guide (for teachers)

A temperature inversion occurs when a layer of warm air sits above cooler air near the ground. Normally warm air rises (convection), mixing pollutants upward and dispersing them. An inversion acts as a lid — pollutants accumulate in the trapped cold layer and cannot escape. Kathmandu's surrounding hills prevent horizontal dispersal as well.

2. Calculate: If Kathmandu's average PM2.5 concentration is 50 µg/m³, how many times higher is it than the WHO annual guideline of 5 µg/m³? [2 marks]

Answer guide (for teachers)

50 ÷ 5 = 10 times higher than the WHO annual guideline. (Note: the 24-hour guideline is 15 µg/m³, which would give 50 ÷ 15 = 3.3 times. Accept either with correct calculation.)

3. Explain why women and children in rural Nepal face a higher health risk from air pollution than adult men in the same household. [4 marks]

Answer guide (for teachers)

Women spend more time cooking near the fire; children spend time in the kitchen. Both are exposed to indoor smoke for many hours daily. Adult men often work outside away from the kitchen. Additionally, children's developing lungs are more vulnerable to PM2.5 damage than adult lungs.

Vocabulary

PM2.5
Particulate matter with diameter less than 2.5 micrometres — fine particles that can penetrate deep into the lungs and enter the blood.
Temperature Inversion
An atmospheric condition where a layer of warm air sits above cooler air, trapping pollutants near the ground.
Air Quality Index (AQI)
A numerical scale from 0 to 500 that translates complex pollution measurements into a single indicator of health risk.
Black Carbon
Fine particles from incomplete combustion of carbon fuels; a major component of soot, a potent short-lived climate pollutant and health hazard.

Extension

Access real-time Nepal air quality data from IQ Air (iqair.com) or Nepal's Department of Environment portal. Compare today's Kathmandu AQI to the reading from our station. Write a paragraph explaining what accounts for any difference between the two readings.

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